Determination of charge-trapping sites in saturated and aromatic polymers by quantum chemical calculation

Takada, Tatsuo; Kikuchi, H.; Miyake, Hiroaki; Tanaka, Yasuhiro; Yoshida, Masafumi; Hayase, Yuji

doi:10.1109/tdei.2015.7076827

Cited by 107 publications

(65 citation statements)

References 9 publications

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“…This effect, observed in previous studies of rGO, [6] zinc oxide, [38] and magnesium oxide [39] NPs, was attributed to the immobilization ("trapping") of charge carriers in deep traps on the rGO interface. This trapping can be attributed to polar groups or adsorbed water on rGO and has previously been explained by the distribution of charges, [40] the induction of dipoles, [41] and the disruption of polymer crystals [42] by the interfacial region of NPs. The EBA composites with 0.5 vol% rGO-APTES ("EBA-0.5-rGO-APTES") and grafted rGO ("EBA-0.5-rGO-PBMA10k", "…50k", "…70k") exhibited similar, or slightly lower, resistivities than neat EBA, which may be explained by the reduced amount of interfacial polar groups and hence the more hydrophobic character of modified rGO.…”

Section: Resultsmentioning

confidence: 93%

Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity

Wåhlander

Nilsson

Andersson

et al. 2017

Macromol. Rapid Commun.

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Field-grading materials (FGMs) are used to reduce the probability for electrical breakdowns in critical regions of electrical components and are therefore of great importance. Usually, FGMs are heavily filled (40 vol.%) with semi-conducting or conducting particles. Here, polymer-grafted reduced graphene oxide (rGO) is used as a filler to accomplish percolated networks at very low filling ratios (<2 vol.%) in a semi-crystalline polymer matrix: poly(ethylene-co-butyl acrylate) (EBA). Various simulation models are used to predict the percolation threshold and the flake-to-flake distances, to complement the experimental results. A substantial increase in thermal stability of rGO is observed after surface modification, either by silanization or subsequent polymerizations. The non-linear DC resistivity of neat and silanized rGO and its trapping of charge-carriers in semi-crystalline EBA are demonstrated for the first time. It is shown that the polymer-grafted rGO improve the dispersibility in the EBA-matrix and that the graft length controls the inter-flake distances (i.e. charge-carrier hopping distances). By the appropriate selection of graft lengths, both highly resistive materials at 10 kV mm and FGMs with a large and distinct drop in resistivity (six decades) are obtained, followed by saturation. The nonlinear drop in resistivity is attributed to narrow inter-flake distance distributions of grafted rGO.

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Section: Resultsmentioning

confidence: 93%

Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity

Wåhlander

Nilsson

Andersson

et al. 2017

Macromol. Rapid Commun.

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“…More computationally efficient linear scaling (LS) methods, like the method implemented in ONETEP, 29 have been developed, and these enable thousands of atoms to be modeled. In DFT simulations, PE is usually modeled as a single isolated oligomeric chain 30,31 or as a fully amorphous or fully crystalline polymer 25 . Only a few studies have previously examined the electronic structure of semicrystalline PE using DFT 14 or other theoretical approaches 9 …”

Section: Introductionmentioning

confidence: 99%

First-principle simulations of electronic structure in semicrystalline polyethylene

Moyassari

Unge

Hedenqvist

et al. 2017

The Journal of Chemical Physics

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In order to increase our fundamental knowledge about high-voltage cable insulation materials, realistic polyethylene (PE) structures, generated with a novel molecular modeling strategy, have been analyzed using first principle electronic structure simulations. The PE structures were constructed by first generating atomistic PE configurations with an off-lattice Monte Carlo method and then equilibrating the structures at the desired temperature and pressure using molecular dynamics simulations. Semicrystalline, fully crystalline and fully amorphous PE, in some cases including crosslinks and short-chain branches, were analyzed. The modeled PE had a structure in agreement with established experimental data. Linear-scaling density functional theory (LS-DFT) was used to examine the electronic structure (e.g., spatial distribution of molecular orbitals, bandgaps and mobility edges) on all the materials, whereas conventional DFT was used to validate the LS-DFT results on small systems. When hybrid functionals were used, the simulated bandgaps were close to the experimental values. The localization of valence and conduction band states was demonstrated. The localized states in the conduction band were primarily found in the free volume (result of gauche conformations) present in the amorphous regions. For branched and crosslinked structures, the localized electronic states closest to the valence band edge were positioned at branches and crosslinks, respectively. At 0 K, the activation energy for transport was lower for holes than for electrons. However, at room temperature, the effective activation energy was very low (∼0.1 eV) for both holes and electrons, which indicates that the mobility will be relatively high even below the mobility edges and suggests that charge carriers can be hot carriers above the mobility edges in the presence of a high electrical field.

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“…This indicates that orbital electrons have low probabilities to distribute the LUMO level. From the previous work, (8) it can be concluded that this HOMO level can be regarded as the conduction level for hole carriers, and this LUMO level is the conduction level for electrons. As for the oxide center chain (C 24 H 48 O), the orbital electrons present a high probability of local distribution around the C=O group at the HOMO and LUMO levels (MO is localized at the C=O group), as shown in Fig.…”

Section: Calculation Methodologymentioning

confidence: 91%

“…The calculation method was also described in a previous work. (8) These basis and calculation functions determine the electronic eigenvalues (energy levels of molecular orbitals) and wave functions. According to these results, various characteristics such as energy level, band structure, electron density, dipole moment, and electric charges are obtained.…”

Section: Calculation Methodologymentioning

confidence: 99%

“…Previous works have studied the charge trapping site in saturated and aromatic polymers by quantum chemical calculation based on the density functional theory (DFT). (7,8) They pointed out that the chemical structures or groups can create trapping sites. From these calculations, the space charge behaviors in lowdensity polyethylene (LDPE), polyimide (Kapton) and ethylene tetrafluoroethylene (ETFE) irradiated by electron beams have been explained.…”

Section: Introductionmentioning

confidence: 99%

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Space Charge of Polyethylene and Electronic Structure Analysis of Trapping Site using Common Chemical Groups

2017

Sensors and Materials

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Pulsed electroacoustic (PEA) measurement technology is widely accepted to detect the space charge distribution inside insulating materials all over the world. In this work, we elucidated further the space charge mechanism based on the typical PEA results of low-density polyethylene (LDPE). Clearly, significant positive accumulation and charge packets are formed inside the sample, which is derived from the chemical and physical structures of polyethylene. Usually, some common chemical groups, such as hydroxyl, carbonyl, double bond, conjugated double bond, and oxide center, exist in polyethylene owing to the manufacturing process and complex ambient. By employing an advanced quantum chemical calculation technique, we obtained the electronic structures of a small polyethylene (PE) chain (C 24 H 50 ) and some PE chains with different chemical groups. After analyzing the electron energy level, molecular orbital, and electric potential, we determined the trapping sites by the chemical groups. These chemical groups with special structures contribute to the narrowing of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gaps (namely, the band gap here), indicating the introduction of trapping levels within the band gap of PE. Additionally, 3D electric potential distributions demonstrate that an obvious potential distortion occurs around these introduced chemical groups. This means that the moving electron or hole carriers can be captured here, leading to the formation of trapped charges. These trapping sites inside the polyethylene are closely related to the space charge accumulation in LDPE.

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Determination of charge-trapping sites in saturated and aromatic polymers by quantum chemical calculation

Cited by 107 publications

References 9 publications

Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity

Reduced and Surface‐Modified Graphene Oxide with Nonlinear Resistivity

First-principle simulations of electronic structure in semicrystalline polyethylene

Space Charge of Polyethylene and Electronic Structure Analysis of Trapping Site using Common Chemical Groups

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